Derek Kirk Kim uses a fun and common conceptual metaphor in today’s installment of his ongoing series “Praxis & Allies” (which you should be reading). Here, the character’s head explodes on discovering his crush actually likes him.
“Conceptual metaphor” is a notion that’s been prevalent in some circles of linguistics for the last 30 years, and is a phenomena where one domain of ideas is mapped onto another. The metaphor that Derek uses is “Emotion is Hot Fluid in a Container” — the emotion constitutes “pressure” in the head (the container) that then can “erupt” when it “overflows.” Emotion isn’t actually hot fluid in a container, but we map the idea of emotions onto the domain of a container.
There have actually been several papers written on this topic with regard to comics, usually describing Anger. The common visual sign of smoke coming out of an angry character’s ears directly links into this “Anger is Hot Fluid in a Container” metaphor. But, here Derek uses it just for an emotional overload. A similar usage was done years ago in Journal Comic by Drew Weing.
As has been argued by many, using these sort of cross-domain metaphors is a great way for the graphic form to visually portray things (like emotions) that aren’t otherwise visible.